Magnetic storage element and magnetic memory

ABSTRACT

A magnetic storage element including a recording layer and a heat generator. The recording layer has a magnetization direction that is configured to change via spin injection so that information can be recorded. The heat generator is positioned to heat the recording layer. The recording layer comprises (i) cobalt and iron and (ii) a non-magnetic element or a non-magnetic element and an oxide.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.13/150,995 filed Jun. 1, 2011, the entirety of which is incorporatedherein by reference to the extent permitted by law. The presentapplication claims the benefit of priority to Japanese PatentApplication No. JP 2010-150179 filed on Jun. 30, 2010 in the JapanPatent Office, the entirety of which is incorporated by reference hereinto the extent permitted by law.

BACKGROUND

The present disclosure relates to non-volatile magnetic storage elementand magnetic memory that perform information recording by spin injectionmagnetization reversal.

The dynamic random access memory (DRAM), which is a high-densityrecording memory capable of high-speed operation, is widely used as arandom access memory in various kinds of information apparatus such ascomputers. However, the DRAM is a volatile memory, in which informationis lost when the power supply is turned off. Therefore, it is desired toput into practical use a non-volatile memory that has performanceequivalent to that of the DRAM and is free from the information loss. Asa candidate for the non-volatile memory, a magnetic random access memory(MRAM) to record information based on the magnetization of a magneticmaterial is attracting attention and its development is being advanced.

The methods for recording of the MRAM include a method of reversingmagnetization by a current magnetic field and a spin injectionmagnetization reversal method of causing magnetization reversal byinjecting spin-polarized electrons directly into the recording layer asdescribed in e.g. Japanese Patent Laid-open No. 2004-193595. This methodis attracting attention because the recording current can be madesmaller as the element size becomes smaller.

SUMMARY

However, in the magnetic memory utilizing the above-described spininjection magnetization reversal method, recording information changesdue to thermal fluctuation and a problem occurs in the recordingretention capability if the element size is reduced. To avoid thisproblem of the lowering of the information retention characteristic dueto thermal fluctuation, it will be important to take a countermeasuresuch as increasing the film thickness of the recording layer.

The current Ic necessary to cause magnetization reversal by spininjection is generally represented by the following equation (1) (referto J. C. Slonzewski, Journal of Magnetism and Magnetic Materials, Volume159 (1996) L1).Ic=α·e·γ·Ms·V·H _(eff)/(g·μ _(B))  (1)

In this equation, α denotes the damping constant, e denotes the chargeof an electron, γ denotes the gyro constant, Ms denotes the saturationmagnetization of the magnetic layer whose magnetization rotates.Further, H_(eff) denotes the effective magnetic field acting on themagnetic layer, such as an anisotropic magnetic field (Ha) due tomagnetic anisotropy and an external magnetic field, V denotes the volumeof the magnetic layer, g denotes the spin injection efficiency, μ_(B)denotes the Bohr magneton.

As is apparent from this equation (1), there is a problem thatincreasing the volume V of the magnetic layer increases the current Icnecessary for spin injection magnetization reversal and leads toincrease in the power consumption. Furthermore, the increase in thepower consumption causes increase in the size of the drive transistor,which makes it difficult to enhance the recording density of themagnetic memory.

There is a desire for the present disclosure to reduce the currentnecessary to cause magnetization reversal by spin injection withoutlowering the information retention characteristic.

According to an embodiment of the present disclosure, there is provideda magnetic storage element including a reference layer configured tohave a magnetization direction fixed to a predetermined direction, arecording layer configured to have a magnetization direction thatchanges due to spin injection in a direction corresponding to recordinginformation, an intermediate layer configured to separate the recordinglayer from the reference layer, and a heat generator configured to heatthe recording layer. A material of the recording layer is such amagnetic material that magnetization at 150° C. is at least 50% ofmagnetization at a room temperature and magnetization at a temperaturein the range from 150° C. to 200° C. is in the range from 10% to 80% ofmagnetization at a room temperature.

According to another embodiment of the present disclosure, there isprovided a magnetic memory including the magnetic storage element havingthe above-described configuration. Specifically, this magnetic memoryincludes a magnetic storage element configured to include a referencelayer having a magnetization direction fixed to a predetermineddirection, a recording layer having a magnetization direction thatchanges due to spin injection in a direction corresponding to recordinginformation, an intermediate layer that separates the recording layerfrom the reference layer, and a heat generator that heats the recordinglayer. Furthermore, the magnetic memory includes two kinds ofinterconnects configured to intersect with each other, and the magneticstorage element is disposed near the intersection of two kinds ofinterconnects and between two kinds of interconnects. In addition, amaterial of the recording layer is such a magnetic material thatmagnetization at 150° C. is at least 50% of magnetization at a roomtemperature and magnetization at a temperature in the range from 150° C.to 200° C. is in the range from 10% to 80% of magnetization at a roomtemperature.

As described above, in the magnetic storage element and the magneticmemory according to the embodiments of the present disclosure, the heatgenerator to heat the recording layer is provided and such a materialthat the temperature characteristic of the magnetization has a specificrange is used as the material of the recording layer. Specifically, sucha material is used that, as this temperature characteristic,magnetization equal to or higher than 50% is obtained at 150° C. andmagnetization in the range from 10% to 80% is obtained at a temperaturein the range from 150° C. to 200° C. on the basis of the magnetizationof the recording layer material at a room temperature.

Employing such a configuration can reduce the current necessary to causemagnetization reversal by spin injection in the magnetic storageelement. In this case, it is possible to perform information rewritingby small current while maintaining the information retentioncharacteristic that is stable against thermal fluctuation and so forth.

According to the magnetic storage element and the magnetic memory of theembodiments of the present disclosure, the current necessary to causemagnetization reversal by spin injection can be reduced without thelowering of the information retention characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of the configuration of amagnetic memory according to an embodiment of the present disclosure;

FIG. 2 is a schematic sectional view of the configuration of a magneticstorage element according to the embodiment of the present disclosure;

FIG. 3 is a schematic sectional view of the configuration of amodification example of the magnetic storage element according to theembodiment of the present disclosure;

FIG. 4 is a schematic sectional view of the configuration of anothermodification example of the magnetic storage element according to theembodiment of the present disclosure;

FIG. 5 is a schematic sectional view of the configuration of anothermodification example of the magnetic storage element according to theembodiment of the present disclosure;

FIG. 6 is a schematic sectional view of the configuration of anothermodification example of the magnetic storage element according to theembodiment of the present disclosure;

FIG. 7 is a diagram showing the temperature dependence of themagnetization of a recording layer in samples 1 to 7 of the magneticstorage element; and

FIG. 8 is a diagram showing the spin injection magnetization reversalcurrent density Jc in samples 1 to 7 of the magnetic storage element oneach element structure basis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Examples of the best mode for carrying out the present disclosure willbe described below with reference to the drawings. The order of thedescription is as follows.

-   1. First Embodiment of the Present Disclosure (embodiment of    magnetic memory)-   2. Second Embodiment of the Present Disclosure (embodiment of    magnetic storage element)-   3. Modification Examples of Second Embodiment of the Present    Disclosure-   4. Working Examples and Comparative Examples    1. First Embodiment of the Present Disclosure (Embodiment of    Magnetic Memory)

First, as a first embodiment of the present disclosure, an embodiment ofa magnetic memory will be described with reference to FIG. 1. As shownin FIG. 1, this magnetic memory 10 includes two kinds of addressinterconnects intersecting with each other, e.g. word lines and bitlines, and is formed by disposing magnetic storage elements 3 near theintersections of these two kinds of interconnects and between theinterconnects. As this magnetic storage element 3, a magnetic storageelement according to an embodiment and modification examples to bedescribed later is used.

In this case, in the area isolated by an element isolating layer 2 in asemiconductor substrate 11 composed of e.g. Si, a drain region 8, asource region 7, and a gate electrode 1 are formed. These componentsconfigure a selection transistor for selecting the correspondingmagnetic storage element 3. The gate electrode 1 serves also as oneaddress interconnect (e.g. word line) extended along the anteroposteriordirection in the diagram. The drain region 8 is formed in common to theselection transistors on the left and right sides in the diagram. Aninterconnect 9 is connected to this drain region 8.

The magnetic storage element 3 is disposed between the source region 7and the other address interconnect (e.g. bit line) 6 that is disposed onthe upper side and extended along the horizontal direction in thediagram. This magnetic storage element 3 includes a recording layerformed of a ferromagnetic layer whose magnetization direction isreversed by spin injection and a heat generator to heat this recordinglayer. As described in detail for the embodiment of the magnetic storageelement to be described later, this recording layer is composed of sucha material that the magnetization at 150° C. is at least 50% of themagnetization at a room temperature and the magnetization at atemperature in the range from 150° C. to 200° C. is in the range from10% to 80% of the magnetization at a room temperature.

This magnetic storage element 3 is disposed near the intersection of thegate electrode 1 and the interconnect 6, which serve as two kinds ofaddress interconnects, and is connected to these interconnects via upperand lower contact layers 4. This makes it possible to apply a current inthe vertical direction to the magnetic storage element 3 via two kindsof interconnects, i.e. the gate electrode 1 and the interconnect 6, andreverse the magnetization direction of the recording layer by spininjection corresponding to information.

The existence of the magnetic storage element 3 having the recordinglayer and the heat generator with the above-described configurationenables this magnetic memory 10 to effectively lower the magnetizationof the recording layer in information recording and perform informationrewriting by small current with keeping of the information retentioncharacteristic that is stable against thermal fluctuation and so forth.

2. Second Embodiment of the Present Disclosure

(Embodiment of Magnetic Storage Element)

One example of a magnetic storage element according to an embodiment ofthe present disclosure will be described below with reference to FIG. 2.As shown in FIG. 2, in this magnetic storage element 30, a base layer 22composed of e.g. Ta serving also as one of the electrodes and anantiferromagnetic layer 23 composed of e.g. PtMn are formed in thatorder over a substrate 21 composed of e.g. thermally-oxidized silicon.Furthermore, a reference layer 24 composed of a ferromagnetic materialsuch as CoFe or CoFeB is stacked on the antiferromagnetic layer 23 andthe magnetization direction of the reference layer 24 is fixed. Over thereference layer 24, a non-magnetic layer 25 composed of e.g. Ru and areference layer 26 composed of a ferromagnetic material such as CoFe orCoFeB are formed in that order. In this case, the reference layer 24 andthe reference layer 26 are coupled to each other with the intermediaryof the non-magnetic layer 25 in such a manner that the magnetizationdirections of these layers are antiparallel to each other, so that asynthetic ferrimagnetic structure is formed. However, the structure isnot limited thereto.

Over the reference layer 26, a recording layer 28 whose magnetizationdirection changes due to spin injection is formed with the intermediaryof an intermediate layer 27 composed of a non-magnetic material. It ispreferable to use e.g. a metal material of small spin scattering such asCu or a ceramic material such as Al₂O₃ or MgO as the material of theintermediate layer 27. In particular, using MgO or the like ispreferable because a large signal is obtained as a reproduction signalin reading. The material of the recording layer 28 will be describedlater.

In this magnetic storage element 30, a heat generator 33 formed of e.g.a thermal resistance layer composed of e.g. Ti is formed on therecording layer 28 formed of a ferromagnetic layer. Furthermore, a caplayer 29 composed of e.g. Ta is formed on this heat generator 33, sothat a multilayer structure part 20 is configured. The planar shape ofthis multilayer structure part 20 may be e.g. an elliptical shape asshown in FIG. 1. However, another planar shape may be employed and thereis no particular limitation. The periphery of this multilayer structurepart 20 is buried in a filling layer 31 composed of a non-magneticmaterial and the surface of the multilayer structure part 20 is flushwith the cap layer 29. On the cap layer 29 and the filling layer 31, anelectrode layer 32 to apply a current to the magnetic storage element 30is formed. In FIG. 2 and FIGS. 3 to 6 to be described later, thedirection of the magnetization possessed by a ferromagnetic layer isschematically shown by an arrowhead.

In this magnetic storage element 30, a voltage is applied between thebase layer 22 and the electrode layer 32 and a current is applied in adirection perpendicular to the film plane of the magnetic storageelement 30 to carry out spin injection, to thereby change the relativeangle between the magnetization directions of the recording layer 28 andthe reference layer 26. Therefore, in the spin injection through thecurrent application, Joule heat due to the applied current is generated,and the influence of the heat generation exists even when the heatgenerator 33 is not provided. However, if the same material as that ofthe related art is used as the magnetic material of the recording layer28, the ratio of contribution to reduction in the spin injection currentby the Joule heat generated in a normal element structure is at anignorable level. In contrast, reduction in the spin injection currentcan be realized by using such a magnetic material that the temperaturedependence of the magnetic characteristics falls within a specific rangeas the material of the recording layer 28 and providing the heatgenerator 33 to aggressively utilize the effect of heat generation.

Specifically, in the present embodiment, as the recording layer 28, sucha magnetic material is used that the magnetization at 150° C. is atleast 50% of the magnetization at a room temperature and themagnetization at a temperature in the range from 150° C. to 200° C. isin the range from 10% to 80% of the magnetization at a room temperature.Due to the use of such a magnetic material, the magnetization of therecording layer 28 is sufficiently lowered when the current necessaryfor spin injection magnetization reversal is applied, and the recordingcurrent is reduced.

If such a magnetic material that the magnetization is lowered to 80% orlower of the magnetization at a room temperature when the temperature ishigher than 200° C. is used as the material of the recording layer 28,the magnetization is not yet sufficiently lowered when the currentnecessary for spin injection magnetization reversal is applied, and theeffect of large reduction in the recording current is not observed.Conversely, if the magnetization of the recording layer 28 is lowered toa value smaller than 50% of the magnetization at a room temperature whenthe temperature is lower than 150° C., a problem occurs in theinformation retention characteristic although the effect of reduction inthe recording current is obtained. Because the magnetic storage element30 of the spin injection type is a non-volatile memory, it should retainthe recorded information for e.g. ten years in a certain temperaturerange. Normally the upper limit of the temperature range is about 90° C.to 120° C. although the temperature range changes depending on the usepurpose. So, information retention tests were made with use of thesetemperatures as the upper limit. As a result, it was found that theoccurrence rate of an information retention error is not sufficientlydecreased if such a magnetic material that the magnetization is loweredto a value smaller than 50% of the magnetization at a room temperaturewhen the temperature is lower than 150° C. is used as the material ofthe recording layer 28.

If the magnetization of the recording layer 28 becomes lower than 10% ofthe magnetization at a room temperature when the temperature is in therange from 150° C. to 200° C., magnetization reversal can be induced bysmall current. However, if such a material that the magnetizationbecomes extremely low is used as the recording layer 28, the backhopping frequently occurs and it is difficult to stably control themagnetization state of the recording layer 28 (refer to e.g. “Journal ofApplied Physics 105, 07D126 (2009)”).

So, in the present embodiment, such a magnetic material that themagnetization at 150° C. is at least 50% of the magnetization at a roomtemperature and the magnetization at a temperature in the range from150° C. to 200° C. is in the range from 10% to 80% of the magnetizationat a room temperature is used as the recording layer 28. Such atemperature characteristic is preferable because it can be easilyrealized by using a material obtained by combining at least one elementof Co and Fe and at least one of a non-magnetic element and an oxide.Examples of the non-magnetic element include Ta, Zr, and V. Examples ofthe oxide include SiO₂, MgO, and Al—O (aluminum oxide). Examples of themagnetic material used as the base include CoFe, CoFeB, and alloyscontaining these substances.

It is preferable that a material layer having a high thermal resistancerate, such as a Ti layer, be provided as the heat generator 33. If sucha thermal resistance material is used as the heat generator 33, heat isgenerated in a certain range when a current is applied. In addition, theconfiguration is simple and the manufacturing is also easy.

The magnetic layers used as the reference layers 24 and 26 and therecording layer 28 may be either an in-plane magnetization film or aperpendicular magnetization film. However, when the reference layers 24and 26 are in-plane magnetization films, an in-plane magnetization filmis employed also as the recording layer 28. Conversely, when thereference layers 24 and 26 are perpendicular magnetization films, it ispreferable to employ a perpendicular magnetization film also as therecording layer 28. As just described, it is preferable that themagnetization directions of the reference layers 24 and 26 and therecording layer 28 be parallel to each other or antiparallel to eachother.

As for the materials of the respective layers configuring the multilayerstructure part 20 except the recording layer 28 and the heat generator33, the same materials as those in the related-art magnetic storageelement of the spin injection type can be used besides theabove-described materials. The same applies also to the film thicknessesthereof and the manufacturing method is also not particularly limited.Furthermore, the same applies also to the substrate 21, the fillinglayer 31, and the electrode layer 32, and the materials andconfigurations thereof are not particularly limited.

3. Modification Examples of Second Embodiment of the Present Disclosure

(3-1) First Modification Example

A first modification example of the magnetic storage element accordingto the second embodiment will be described below with reference to FIG.3. As shown in FIG. 3, in this magnetic storage element 50, a heatgenerator 53 is formed on a substrate 41. Over the heat generator 53, abase layer 42, an antiferromagnetic layer 43, a reference layer 44, anon-magnetic layer 45, a reference layer 46, an intermediate layer 47formed of a non-magnetic layer, a recording layer 48, and a cap layer 49are formed in that order. The heat generator 53 is formed of e.g. athermal resistance layer. The respective layers from the heat generator53 to the cap layer 49 are formed with e.g. an elliptical shape as theirplanar shape, so that a multilayer structure part 40 is configured.Furthermore, a filling layer 51 is formed around the multilayerstructure part 40 and an electrode layer 52 is formed on the cap layer49 and the filling layer 51. Also in this example, as the material ofthe recording layer 48, such a magnetic material is used that themagnetization at 150° C. is at least 50% of the magnetization at a roomtemperature and the magnetization at a temperature in the range from150° C. to 200° C. is in the range from 10% to 80% of the magnetizationat a room temperature. The materials and film thicknesses of therespective other layers configuring the multilayer structure part 40except the heat generator 53 may be the same as those of the related-artmagnetic storage element of the spin injection type, and themanufacturing method thereof is also not particularly limited. The sameapplies also to the substrate 41, the filling layer 51, and theelectrode layer 52, and the materials and configurations thereof are notparticularly limited.

In the examples shown in FIG. 2 and FIG. 3, the reference layers 24, 26,44, and 46 are disposed closer to the substrates 21 and 41 than therecording layers 28 and 48. However, the structure is not limitedthereto. For example, the same characteristics can be achieved also witha reverse structure in which the recording layers 28 and 48 are disposedcloser to the substrates 21 and 41 and the reference layers 24, 26, 44,and 46 are disposed closer to the electrode layers 32 and 52 on theupper side.

(3-2) Second Modification Example

A second modification example of the magnetic storage element accordingto the second embodiment will be described below with reference to FIG.4. In the example shown in FIG. 4, a magnetic storage element 90 has aso-called dual configuration in which reference layers 66 and 76 areprovided below and over a recording layer 68 with the intermediary ofintermediate layers 67 and 77 formed of non-magnetic layers. In thismagnetic storage element 90, over a substrate 61, a base layer 62, anantiferromagnetic layer 63, a reference layer 64, a non-magnetic layer65, the reference layer 66, the intermediate layer 67 formed of anon-magnetic layer, and the recording layer 68 are formed in that order.Furthermore, over the recording layer 68, the intermediate layer 77formed of a non-magnetic layer, the reference layer 76, a non-magneticlayer 75, a reference layer 74, a non-magnetic layer 85, a referencelayer 84, and an antiferromagnetic layer 83 are formed in that order.Over the antiferromagnetic layer 83, a heat generator 93 formed of e.g.a thermal resistance layer is formed. In addition, a cap layer 89 isformed on the heat generator 93, so that a multilayer structure part 60is configured. A filling layer 91 is formed around the multilayerstructure part 60 and an electrode layer 92 is formed on the cap layer89 and the filling layer 91. Also in this example, as the material ofthe recording layer 68, such a magnetic material is used that themagnetization at 150° C. is at least 50% of the magnetization at a roomtemperature and the magnetization at a temperature in the range from150° C. to 200° C. is in the range from 10% to 80% of the magnetizationat a room temperature. The materials and film thicknesses of therespective other layers configuring the multilayer structure part 60except the heat generator 93 may be the same as those of the related-artmagnetic storage element of the spin injection type, and themanufacturing method thereof is also not particularly limited. The sameapplies also to the substrate 61, the filling layer 91, and theelectrode layer 92, and the materials and configurations thereof are notparticularly limited.

(3-3) Third Modification Example

A third modification example of the magnetic storage element accordingto the second embodiment will be described below with reference to FIG.5. In the example shown in FIG. 5, a magnetic storage element 130 alsohas a dual configuration in which reference layers 106 and 116 areprovided below and over a recording layer 108 with the intermediary ofintermediate layers 107 and 117 formed of non-magnetic layers, similarlyto the second modification example. However, a heat generator 133 isprovided between a substrate 101 and a base layer 102. In this magneticstorage element 130, over the substrate 101, the heat generator 133formed of e.g. a thermal resistance layer, the base layer 102, anantiferromagnetic layer 103, a reference layer 104, a non-magnetic layer105, the reference layer 106, the intermediate layer 107 formed of anon-magnetic layer, and the recording layer 108 are formed in thatorder. Furthermore, over the recording layer 108, the intermediate layer117 formed of a non-magnetic layer, the reference layer 116, anon-magnetic layer 115, a reference layer 114, a non-magnetic layer 125,a reference layer 124, and an antiferromagnetic layer 123 are formed inthat order. In addition, a cap layer 129 is formed on theantiferromagnetic layer 123, so that a multilayer structure part 100 isconfigured. A filling layer 131 is formed around the multilayerstructure part 100 and an electrode layer 132 is formed on the cap layer129 and the filling layer 131. Also in this example, as the material ofthe recording layer 108, such a magnetic material is used that themagnetization at 150° C. is at least 50% of the magnetization at a roomtemperature and the magnetization at a temperature in the range from150° C. to 200° C. is in the range from 10% to 80% of the magnetizationat a room temperature. The materials and film thicknesses of therespective other layers configuring the multilayer structure part 100except the heat generator 133 may be the same as those of therelated-art magnetic storage element of the spin injection type, and themanufacturing method thereof is also not particularly limited. The sameapplies also to the substrate 101, the filling layer 131, and theelectrode layer 132, and the materials and configurations thereof arenot particularly limited.

(3-4) Fourth Modification Example

A fourth modification example of the magnetic storage element accordingto the second embodiment will be described below with reference to FIG.6. In this example, as shown in FIG. 6, reference layers 144 and 146 areprovided on a single side of a recording layer 148 similarly to theexamples shown in FIG. 2 and FIG. 3. However, in this example, a heatgenerator 153 is provided on a filling layer 151 separately from amultilayer structure part 140. In this magnetic storage element 150,over a substrate 141, a base layer 142, an antiferromagnetic layer 143,the reference layer 144, a non-magnetic layer 145, the reference layer146, an intermediate layer 147 formed of a non-magnetic layer, therecording layer 148, and a cap layer 149 are formed in that order. Therespective layers from the base layer 142 to the cap layer 149 areformed with e.g. an elliptical shape as their planar shape, so that themultilayer structure part 140 is configured. Furthermore, the fillinglayer 151 is formed around the multilayer structure part 140 and anelectrode layer 152 is formed on the cap layer 149 and the filling layer151. Moreover, at a position close to the multilayer structure part 140on the filling layer 151, the heat generator 153 is formed e.g. at aposition adjacent to the electrode layer 152. The heat generator 153 isformed of e.g. a thermal resistance layer. Also in this example, as thematerial of the recording layer 148, such a magnetic material is usedthat the magnetization at 150° C. is at least 50% of the magnetizationat a room temperature and the magnetization at a temperature in therange from 150° C. to 200° C. is in the range from 10% to 80% of themagnetization at a room temperature. The materials and film thicknessesof the respective other layers configuring the multilayer structure part140 except the heat generator 153 may be the same as those of therelated-art magnetic storage element of the spin injection type, and themanufacturing method thereof is also not particularly limited. The sameapplies also to the substrate 141, the filling layer 151, and theelectrode layer 152, and the materials and configurations thereof arenot particularly limited.

In the above-described magnetic storage elements 90 and 130 of thesecond and third modification examples according to the secondembodiment, as the configuration of the reference layers, two magneticmaterial layers and one non-magnetic material layer are disposed in thelower part (substrate side) and three magnetic material layers and twonon-magnetic material layers are disposed in the upper part (oppositeside to the substrate). However, the configuration is not limitedthereto. The lower part and the upper part may be interchanged, and onemagnetic material layer may be employed as the reference layer.Furthermore, the numbers and combination of the magnetic material layersare not particularly limited. For example, the numbers of magneticmaterial layers of the upper part and the lower part may be one and two,respectively, or three and four, respectively.

In all of the above-described magnetic storage elements 30, 50, 90, 130,and 150 shown in FIGS. 2 to 6, the heat generator is provided in themultilayer structure part or on the filling layer surrounding themultilayer structure part. In any example, heat generated by the heatgenerator reaches the recording layer and the amount of heat generationper unit current is increased compared with the case of providing noheat generator. Thus, the temperature rise of the recording layer islarger compared with the case of providing no heat generator. Therefore,in spin injection, the magnetization is reduced compared with themagnetization at a room temperature. Thus, for example even when thevolume of the recording layer is increased to enhance the informationretention characteristic, increase in the spin injection magnetizationreversal current can be avoided. This can provide magnetic storageelement and magnetic memory in which the spin injection magnetizationreversal current is reduced without the lowering of the informationretention stability. In the case of the element structure in which theheat generator is provided in the multilayer structure part as shown inFIGS. 2 to 5, the distance between the recording layer and theupper/lower electrode serving as a heat sink is longer and thetemperature rise of the recording layer is larger compared with theexample shown in FIG. 6. Specifically, in the case of the fourthmodification example, in which the heat generator 153 is provided on thefilling layer 151 as shown in FIG. 6, the temperature rise of therecording layer 146 is smaller than that in the other examples but theabove-described effect due to the temperature rise is sufficientlyobtained.

4. Working Examples and Comparative Examples

Working examples and comparative examples of the present disclosure willbe described below. First, to confirm the advantageous effect of theembodiments of the present disclosure, recording layers composed ofmagnetic materials shown in the following Table 1 were fabricated andthe temperature dependence of the magnetization was evaluated. Samples 1to 7 described in Table 1 show the materials configuring the recordinglayer and the total film thicknesses (unit: nm) of the respectivematerials.

TABLE 1 Sample Base Magnetic Non-magnetic Number Material Layer OxideRemarks #1 CoFeB: 2.5 — — comparative example #2 CoFeB: 3 Ta: 0.4 —working example #3 CoFeB: 3 Zr: 0.3 SiO₂: 0.3 working example #4 CoFeB:4 Ta: 0.5 MgO: 0.8 working example #5 CoFeB: 4 V: 0.7 Al—O: 0.3 workingexample #6 CoFeB: 4 V: 0.5 — comparative example #7 CoFeB: 4 Ta: 0.5SiO₂: 0.8 comparative example

The composition of CoFeB used as the base magnetic material in samples 1to 7 is as follows: Co is 40 atomic %, Fe is 40 atomic %, and B is 20atomic %. However, the recording layer used in the embodiments of thepresent disclosure is not limited to the material having thiscomposition ratio. Samples 2 to 7 are configured by stacking the basemagnetic material and a non-magnetic layer and/or an oxide. Themultilayer configurations of the respective samples are as follows.Specifically, regarding the respective samples, the film thicknesses andthe numbers of stacked layers about the base magnetic material, thenon-magnetic layer, and the oxide, and the multilayer configuration fromthe substrate side (i.e. the intermediate layer side) are shown. Thenumeric value in the bracket in the multilayer configuration indicatesthe film thickness and the unit thereof is nm.

-   [Sample 2: CoFeB (1 nm)×three layers, Ta (0.2 nm)×two layers]    CoFeB (1)/Ta (0.2)/CoFeB (1)/Ta (0.2)/CoFeB (1)-   [Sample 3: CoFeB (1 nm)×three layers, Zr (0.15 nm)×two layers, SiO₂    (0.15 nm)×two layers]    CoFeB (1)/SiO₂ (0.15)/Zr (0.15)/CoFeB (1)/Zr (0.15)/SiO₂    (0.15)/CoFeB (1)-   [Sample 4: CoFeB (1 nm)×four layers, Ta (0.25 nm)×two layers, MgO    (0.2 nm)×one layer, MgO (0.3 nm)×two layers]    CoFeB (1)/MgO (0.2)/CoFeB (1)/Ta (0.25)/MgO (0.3)/CoFeB (1)/MgO    (0.3)/Ta (0.25)/CoFeB (1)-   [Sample 5: CoFeB (1 nm)×four layers, V (0.3 nm)×one layer, V (0.2    nm)×two layers, Al—O (0.15 nm)×two layers]    CoFeB (1)/Al—O (0.15)/CoFeB (1)/V (0.2)/Al—O (0.15)/V (0.2)/CoFeB    (1)/V (0.3)/CoFeB (1)-   [Sample 6: CoFeB (1 nm)×four layers, V (0.2 nm)×one layer, V (0.15    nm)×two layers]    CoFeB (1)/V (0.15)/CoFeB (1)/V (0.2)/CoFeB (1)/V (0.15)/CoFeB (1)-   [Sample 7: CoFeB (1 nm)×four layers, Ta (0.25 nm)×two layers, SiO₂    (0.4 nm)×one layer, SiO₂ (0.2 nm)×two layers]    CoFeB (1)/SiO₂ (0.2)/Ta (0.25)/CoFeB (1)/SiO₂ (0.4)/CoFeB (1)/Ta    (0.25)/SiO₂ (0.2)/CoFeB (1)

FIG. 7 shows the temperature dependence of the magnetization Mst of therecoding layer in these samples 1 to 7. In the recording layer insamples 2 to 5, the magnetization at 150° C. is at least 50% of themagnetization at a room temperature and the magnetization at atemperature in the range from 150° C. to 200° C. is in the range from10% to 80% of the magnetization at a room temperature. Thus, therecording layers in samples 2 to 5 correspond to the working examples ofthe present disclosure. On the other hand, the recording layers insamples 1, 6, and 7 correspond to the comparative examples.

Next, the difference between the case of providing no heat generator andthe case of providing the heat generator was investigated for thepurpose of confirming the advantageous effect of the embodiments of thepresent disclosure. For this investigation, the magnetic layer materialsof the recording layers in samples 1 to 7 shown in Table 1 were used. Asconfiguration examples of the magnetic storage element, theabove-described configurations of FIG. 2, FIG. 3, and FIG. 6 wereemployed as a configuration “with the heat generator,” and theconfiguration obtained by omitting the heat generator in FIG. 2 wasemployed as a configuration “without the heat generator.” Based on theseconfiguration examples, the spin injection magnetization reversalcharacteristic was evaluated. The materials and configurations of therespective components are as follows:

Substrate: thermally-oxidized Si substrate

Base layer: Ta, thickness 5 nm

Antiferromagnetic layer: PtMn, thickness 30 nm

Reference layer (lower layer): CoFe, thickness 2 nm

Non-magnetic layer: Ru, thickness 0.8 nm

Reference layer (upper layer): CoFeB, thickness 2 nm

Intermediate layer: MgO, thickness 1.0 nm

Recording layer: configurations in samples 1 to 7 in Table 1

Cap layer: Ta, thickness 5 nm

Electrode layer: Al—Cu, thickness 100 nm

Filling layer: SiO₂, thickness 10 to 100 nm

As the heat generator, Ti, which is a metal having a low thermalconductivity, was used with a film thickness of 80 nm. When a metalhaving a low thermal conductivity like Ti is used, large heat generationis obtained. The shape of the multilayer structure part of the magneticstorage element was set to an elliptical shape with a 100-nm-lengthminor axis and a 200-nm-length major axis.Jc=Ic/A

(A: the area of the magnetic storage element (=the cross-sectional areain a direction perpendicular to the film plane))

That is, the following equation (2) is obtained from the above-describedequation (1).Jc=α·e·γ·Ms·V·H _(eff)/(g·μ _(B) ·A)  (2)

In equation (2), α denotes the damping constant. e denotes the charge ofan electron. γ denotes the gyro constant. Ms denotes the saturationmagnetization of the magnetic layer whose magnetization rotates. H_(eff)denotes the effective magnetic field acting on the magnetic layer, suchas an anisotropic magnetic field (Ha) due to magnetic anisotropy and anexternal magnetic field. V denotes the volume of the magnetic layer. gdenotes the spin injection efficiency. μ_(B) denotes the Bohr magneton.

In FIG. 8, “WITHOUT HEAT GENERATOR” corresponds to the element structureobtained by omitting the heat generator 33 in the element configurationshown in FIG. 2. “WITH HEAT GENERATOR OVER RECORDING LAYER” correspondsto the element structure shown in FIG. 2. “WITH HEAT GENERATOR BELOWREFERENCE LAYER” corresponds to the element structure shown in FIG. 3.“WITH HEAT GENERATOR NEAR FILLING LAYER” corresponds to the elementstructure shown in FIG. 6.

From the result of FIG. 8, it turns out that the spin injectionmagnetization reversal current Jc can be suppressed to 4.0 MA/cm² orlower in samples 2 to 5, which correspond to the working examples of thepresent disclosure. In these samples 2 to 5, the magnetization in spininjection is reduced and the spin injection magnetization reversalcurrent can be reduced. It turns out that particularly in the elementstructure in which the heat generator is provided in the multilayerstructure part, the spin injection current is reduced compared with thecase of providing the heat generator on the filling layer. Furthermore,it turns out that the spin injection magnetization reversal currentdensity Jc can be decreased at the most degree in the elementconfiguration in which the heat generator is provided over the recordinglayer.

The material of the recording layer used in samples 1 to 7 was soadjusted that the thermal stability index A fell within the range of 50to 55. In the spin injection magnetization reversal current density Jcof the recording layer in sample 1, large change dependent on theelement structure is not found. In contrast, in the recording layer insamples 2 to 7, the spin injection magnetization reversal currentdensity Jc in the element structure including the heat generator isdecreased by at least 10% compared with the element structure includingno heat generator, so that the advantageous effect of the embodiments ofthe present disclosure is confirmed.

As another experiment, the information retention rate under a 120° C.environment and the occurrence rate of back hopping were measuredregarding samples 1 to 7. The experimental result is shown in thefollowing Table 2.

TABLE 2 Information Occurrence Retention Rate Rate of Sample under 120°C. Back Number Environment Hopping Remarks #1  ~100% <1% comparativeexample #2  ~100% <1% working example #3  ~100% <1% working example #4 ~100% <1% working example #5  ~100% <1% working example #6 ~99.9% 13%comparative example #7   ~80% 13% comparative example

According to the result of FIG. 8, the spin injection magnetizationreversal current density Jc can be decreased also in samples 6 and 7.However, as is apparent from Table 2, the information retention rate islowered and the occurrence rate of back hopping is increased in samples6 and 7. That is, it turns out that the controllability of themagnetization reversal behavior is deteriorated in samples 6 and 7. Inview of the above-described result and the result about the temperaturedependence shown in FIG. 7, it turns out that it is preferable for themagnetic material of the recording layer to have the followingtemperature characteristic. Specifically, it is preferable to use, asthe recording layer, such a magnetic material that the magnetization at150° C. is at least 50% of the magnetization at a room temperature andthe magnetization at a temperature in the range from 150° C. to 200° C.is in the range from 10% to 80% of the magnetization at a roomtemperature. Using a magnetic material having such a temperaturecharacteristic as the recording layer can decrease the magnetization inspin injection by heating from the heat generator and thereby suppressincrease in the spin injection magnetization reversal current Ic evenwhen the film thickness is increased to some extent in order to maintainthe information retention characteristic. The recording layer materialfrom which such a temperature characteristic is obtained is not limitedto the materials and configurations in the above-described samples 2 to5. It should be obvious that the material and composition ratio of thebase magnetic material, the materials and film thicknesses of thenon-magnetic material and the oxide, and the number of stacked layersand the multilayer configuration can be properly changed and the sameadvantageous effect can be achieved as long as a material having theabove-described temperature dependence of the magnetization is employed.

The present disclosure contains subject matter related to that disclosedin Japanese Priority Patent Application JP 2010-150179 filed in theJapan Patent Office on Jun. 30, 2010, the entire content of which ishereby incorporated by reference.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

What is claimed is:
 1. A magnetic storage element comprising: arecording layer with a magnetization direction that changes via spininjection; and a heat generator positioned to heat the recording layer,wherein, the recording layer comprises (i) cobalt and iron and (ii) anon-magnetic element or a non-magnetic element and an oxide, wherein: amagnetization of the recording layer at 150° C. is at least 50% of itsmagnetization at room temperature, and the magnetization of therecording layer at a temperature in a range from 150° C. to 200° C. isin a range of 10% to 80% of its magnetization at the room temperature.2. The magnetic storage element of claim 1, wherein the recording layercomprises at least (a) a CoFeB layer and (b) a layer with thenon-magnetic element.
 3. The magnetic storage element of claim 1,wherein the recording layer comprises (a) a CoFeB layer, (b) a layerwith the non-magnetic element, and (c) an oxide layer.
 4. The magneticstorage element of claim 1, wherein the heat generator comprises atitanium layer.
 5. The magnetic storage element of claim 1, wherein theheat generator is in contact with the recording layer.
 6. The magneticstorage element of claim 1, wherein the heat generator does not overlapthe recording layer.
 7. A magnetic storage element comprising: arecording layer with a magnetization direction that changes via spininjection; a heat generator positioned to heat the recording layer, theheat generator being a thermal resistance layer comprising titanium; anda cap layer over the recording layer, the cap layer being distinct fromthe heat generator, wherein: a magnetization of the recording layer at150° C. is at least 50% of its magnetization at room temperature, andthe magnetization of the recording layer at a temperature in a rangefrom 150° C. to 200° C. is in a range of 10% to 80% of its magnetizationat the room temperature.
 8. The magnetic storage element of claim 7,wherein the recording layer comprises (i) cobalt and iron and (ii) anon-magnetic element or a non-magnetic element and an oxide.
 9. Themagnetic storage element of claim 7, wherein the recording layercomprises (a) a CoFeB layer, (b) a layer with a non-magnetic element,and (c) an oxide layer.
 10. The magnetic storage element of claim 7,further comprising: a reference layer with a magnetization directionthat is fixed in a predetermined direction, wherein, the reference layeris between the recording layer and the heat generator.
 11. A magneticstorage element including (a) a recording layer with a magnetizationdirection that changes via spin injection, and (b) a heat generatorpositioned to heat the recording layer, wherein, the recording layercomprises (i) cobalt and iron and (ii) a non-magnetic element or anon-magnetic element and an oxide, wherein a magnetization of therecording layer at 150° C. is at least 50% of its magnetization at roomtemperature, and the magnetization of the recording layer at atemperature in a range from 150° C. to 200° C. is in a range of 10% to80% of its magnetization at the room temperature.
 12. The magneticmemory of claim 11, wherein the heat generator is a thermal resistancelayer comprising titanium.
 13. The magnetic memory of claim 11, furthercomprising: a reference layer with a magnetization direction that isfixed in a predetermined direction.
 14. The magnetic memory of claim 11,further comprising: a reference layer with a magnetization directionthat is fixed in a predetermined direction, wherein, the reference layerand the recording layer are stacked in a multilayer structure within afilling layer, and the heat generator is disposed on the filling layer.